A drilling procedure is usually accompanied by small-sized particle residues extracted from the drilled material e.g. dust, sawdust, metal particles, etc. The vibrations associated with the operation of a power drill and the rotation of the cutting tool tend to vigorously disperse these residues all around the working environment, forcing the user to clean and remove the scattered dust and residues.
It is therefore known to provide either a dust collector, which is inherently of a passive type, or a dust extractor, which is inherently of an active type. Representative patents relating to dust collectors include U.S. Pat. Nos. 6,102,631; 4,251,171; 5,061,123 and 5,653,561. The devices described in these patents typically include a receptacle mounted on the drill bit having an open end that is held flush with a work surface being drilled. However, they oblige a hermetically sealed boundary with the drilled zone and are highly affected by gravity (i.e. drilling orientation), especially when detaching the drill from the drilled zone.
Dust-extraction type devices require suction for generating a flow of air from the drilling zone through the extraction device/apparatus. U.S. Pat. Nos. 5,605,421 and 4,184,226 disclose extractors that rely on external vacuum sources and are thus not standalone devices. U.S. Pat. Nos. 7,455,486 and 5,090,499 disclose devices having an independent, integrated electrically-operated suction element which extends up to the drilling zone and can be jointed externally to the drill body.
In order to obviate the need for a separate power source, it is known to utilize the drive of the power-tool motor as the driving force for the suction element. U.S. Pat. Nos. 6,848,985; 6,514,131 and 7,497,886 make use of a fan located internally to the power-tool housing and mounted on its motor drive-shaft. Some of these devices compel an inherent alteration in the power-tool design and manufacture and thus exclude their implementation on existing, standard power-tools.
U.S. Pat. No. 3,850,254 discloses a dust extractor drilling apparatus which includes a fan driven by a friction wheel operatively connected to the chuck of the drill. In this case the fan is not driven directly via the rotating chuck but rather via a transmission gear system. It also necessitates the use of a telescopic sleeve which surrounds the tip of the drilling tool.
U.S. Pat. No. 7,510,356 discloses a drill bit made of a shaft including a fan on the shaft and a related drill attachment for dust collection made of a handle. It excludes the use of existing, standard cutting-tools.
It would therefore be desirable to provide a dust extractor for a power drill that relies solely on the rotation of the drill bit and requires no coupling, directly or indirectly, to the drill body or to its motor and that is suitable for use for any drill bit.
U.S. Pat. No. 5,772,367 addresses this requirement and discloses an attachment for a rotating tool bit which provides air flow in the vicinity of the work area without the need for separate vacuum or compressed air supplies. The device is mounted on the shaft of the rotating tool bit and has a plurality of vanes which direct airflow through a cylindrical casing towards or away from the work area. A central aperture provides resilient mounting of the attachment to the tool bit whereby rotation of the tool bit induces rotation of the complete attachment.
The device described in U.S. Pat. No. 5,772,367 is standalone and requires no external source of power being mounted on the shank of a drill bit. But it also suffers from the following drawbacks. The device comprises a casing fixed to a base plate, which is integral with a central tube mounted on the drill bit and to which there are fixed a plurality of impellers that extend radially outward from the central tube. The impellers define radial channels around the periphery of the device and are shaped to suck in air and debris at a front end of the device, which is then discharged through the radial channels at the side edge of the device where it is collected by an annular filter.
Since the impellers are integral with the base plate, which itself is integral with the conical casing, rotation of the casing induces rotation of the impellers relative to the exterior of the casing. In other words, the complete attachment including the casing and the impellers rotates as a single unit, there being no relative rotation between the impellers and the side wall of the casing. This limits the suction efficiency of the device since once air is sucked into the front end of the conical casing, there does not appear to be a mechanism that directs the air and debris toward the annular filter other than the centrifugal force of the rotating casing.
Also, since the entire attachment including the casing and the impellers rotates as a single unit, there is generated a large torque/moment which potentially can impose a risk for the operator. Additionally, once the drill bit is rotating, the attachment cannot be handled so that the operator cannot change its location on the shaft of the tool bit. Also since the casing is rotating, the attachment cannot be brought too close to the workpiece because it will frictionally swivel and scratch the workpiece surrounding surface.
Furthermore, the device is frictionally gripped by the shank of the drill bit close to the chuck such that the air inlet is necessarily maintained remote from the workpiece and the suction applied by the rotating impellers is applied over a larger distance. The consequent reduction in suction is addressed by providing a conical casing at a front end of the device, which may be telescopically extended so that the tip of the casing is proximate to the workpiece. But while the conical casing may assist in channeling air through the device, it does not change the fact that the suction source is remote from the workpiece. Moreover, even when fully contracted the length of the casing extends along the cutting flute of the drill bit, which significantly reduces its effective length and limits the depth of penetration into the workpiece.
Finally, in order to be suitable for use with drills of different diameter, a central tube of the device is provided with a resilient elastomeric material that provides frictional engagement with the outer surface of drill bits of different diameters. By such means the central tube is gripped by the rear shank of the drill bit. This “one size fits all” is clearly a limitation since it is hardly practicable that the resilient material will be capable of accommodating drill bits across the complete range of the chuck, typically from less than 1 mm to 13 mm.